measuring thermal conductivity of pcms
Post on 23-Feb-2022
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Measuring thermal conductivity of PCMs
Common method: - Laser Flash measurement
Problems: - Sample can‘t be measured as solid AND melt
- Indirect determination of thermal conductivity
(measurement of thermal diffusivity)
Alternative:
What means THB
Transient Hot Bridge
The Transient Hot Bridge method, which is used to measure the thermal transport properties of
materials, is an enhancement of the Hot Wire or the Transient Hot Strip method (DIN EN 993-14, DIN
EN 993-15). The measuring methods mentioned are transient, time depended measuring methods.
The advantage of these methods compared to stationary methods is a much shorter measuring time,
and the thermal diffusivity is measured in parallel to the thermal conductivity.
Steady state: • Guarded Hot Plate (GHP)
Transient state: • Hot probe
• hot wire, hot strip
• hot plane, hot disk®
• Laser flash
• Short measuring time
• simple preparation
• small samples
• complex evaluation
• Clear mean, simply evaluation of the l and
its dl
• long measuring time
• sample preparation
• complex realization
Two types of absolute
measurements
T
Transient state methods
Sample
q = P
Heat source and temperature probe
Sample
2
0r
ta
The value of the thermal conductivity l is nearly inversely proportional to temperature rise.
Diffusivity a determines measurement duration, the needed time to reach the steady state.
T
l F
TL
Pm
0~
Hot strip
•-- end effect
•-- longer measuring time
•-- smaller strip resistance
•-- worse signal- noise ratio
Improvements for THS-method
Plane design like electronic boards
Film technology like heat foils fabrication
Two part (tandem) strip with short part as “guard heater”
Bridge circuit integrated
Signal form with two well solved characteristic parameter
for thermal conductivity und diffusivity
Tandem Strip
+ easy production
+ end-effect free
+ high electrical resistance
-- more electronic complexity
Improved Hot Strip
Improvements for THS-method
THB Specification
10%
(QSS)
< 5%
(QSS)
< 3 %
<10%
Fritt
< 5%
Sample Holder Solids
Sensor sandwiched between
two PMMA samples Sample holder
for defined
sample pressure
Hot Point Sensor
• 0.02 to 30 W/m*K • -150 to 700 °C • Small samples (3x3x3 mm) • Reactive Samples (e.g. epoxy resins) • Anisotropic Samples
QSS- Sensor
QSS Sensor
• Up to 500 W/m*K
• New Patented Methode
• Real Measurement of λ
Fritt Sensor
Fritt Sensor
• Gases
• Liquids
Without Convection
• Calorimeter for Liquids
with QSS- Sensor
High Temperature Sensor
High Temperature Hot Point Sensor
• -150 to 700 °C
• 0,01 to 30 W/m*K
• Minimum sample size:
3x3x1 mm
Problem: - System must be able to measure solids, melts and liquids - Temperature regulation must be possible with highest precision - Special furnace is needed
Application PCM Materials
Linseis THB Furnace for PCM Materials
Linseis THB Furnace for PCM Materials
- Temperature Range from -150°C to 700°C
- Temperature adjustment with high accuracy
- usable with all types of Sensors
- closed measurement chamber
New THB Software
• Automatic Calibration
• Calculation of Thermal Penetration Depth
• Calculation of Effusivity and Specific heat Capacity
• Optimized Data Evaluation
• Data Base Link with Reference Materials
• Report Generator
• Data Export
THB Main Benefits
Measure simultaneously and precise both values:
thermal conductivity and diffusivity
Quick experimental runs from seconds to a few minutes.
Typical uncertainty for most materials better than 3 % (k = 2).
Solid, Liquid loose samples
Anisotropic Samples can be measured
Range for Thermal Conductivity: 0,01 to 500 W/m*K
Self optimized measurements
No special knowledge or skills needed
Robust design suitable for many industrial applications.
Automatically error detection of, e.g., poor thermal contact and temperature instability.
Thank you for your attention !
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